Field of the Invention
Electromechanical actuators and, in particular, position sensing and motor commutation in electromechanical actuators.
Description of Related Art
Brushless direct current (BLDC) motors are a form of electric motor, where a current is passed through, e.g., a series of solenoids to provide a motivating force. Coordinating the motion of the motor with the application of current to the solenoids is called commutation, a function which has traditionally been performed with the use of Hall Effect sensors to determine when current should be applied to a given solenoid.
Fine, incremental, position sensing has been performed using optical encoding, but needs to reestablish an origin on every loss of power. Position sensing can also be performed using absolute analog sensors like potentiometers. However, potentiometers usually have a sliding or rolling contact, which makes them susceptible to wear over long-term use. Furthermore, analog devices are inherently noisy, leading to positional inaccuracies, and their output must be also be digitized to be useful, which limits resolution. Some digital, absolute position sensors have been proposed that make use of separate power supplies to maintain their absolute position after an origin is established. Others make use of computationally inefficient lookup tables that map the unique states of a sensor to a unique position over multiple turns. These solutions are both complex and costly to manufacture.
The inclusion of analog position sensors renders the motor susceptible to electrical noise and wear, generally reducing the accuracy, and decreasing the potential life of the device. Furthermore, conventional solutions that are based on incremental position encoders need to perform a homing operation upon power-up, causing both delay and motion that may be detrimental to real-time control applications.